The present invention relates to scratch-resistant coatings for plastic optical elements. In particular, the present invention relates to a method of forming a scratch-resistant coating on a plastic ophthalmic lens, and the lenses formed by that process.
Plastic ophthalmic lenses have become increasing popular because of their lighter weight, reduced bulk and greater shatter resistance than glass lenses. One commonly used monomer system for forming plastic ophthalmic lenses is allyl diglycol carbonate (which is sold under the trademark CR-39).
CR-39 plastic ophthalmic lenses are relatively hard and scratch-resistant when compared to other plastic ophthalmic lenses. The scratch resistance of CR-39 lenses, however, is lower than that of glass. As a result, there has been significant effort expended to develop scratch-resistant coatings for plastic ophthalmic lenses.
A wide variety of different coating techniques and materials have been proposed over the years. These include applying coating solutions by spin, dip, spray or flow coating. In recent years, considerable effort has been expended in developing "in-mold" coating techniques, in which a coating is applied to a surface of a mold and then transferred to the lens as the lens monomer is cured in the mold.
One coating component which has been proposed by a number of different workers for scratch-resistant coating compositions is "PETA" (pentaerythritol tri- or tetra-acrylate. This component is discussed, for example, in Oshima et al. U.S. Pat. No. 3,968,305, Russell U.S. Pat. No. 4,338,269, Sandvig et al U.S. Pat. No. 4,544,572 and Carmelite et al U.S. Pat. No. 4,774,035.